A common practice in forming fibers of mineral material is to pass the material in a molten state through the orifices of the peripheral wall of a centrifuge or spinner to create primary fibers. Thereafter, the primary fibers are further attenuated into a veil of secondary fibers of smaller diameter by the action of a flow of gases discharged downwardly from an annular blower. It is known that such blowers can be adapted with a Coanda surface and can be adapted to blow air, steam or other gases. The Coanda blowers of the prior art are commonly comprised of a concave body member and a cantilevered lid member mounted to the body member, where the free end of the cantilevered member is close to the Coanda surface on the body member to define a narrow slot for the discharge of gases from the blower.
One of the problems associated with the blowers of the fiber-forming devices of the prior art is that it is difficult to accurately control the width of the slot in the high temperature environment in which the blower must operate. The high operating temperatures have a tendency to deform the cantilevered lid member, thereby modifying the size and the shape of the slot and resulting in non-uniform secondary attenuation of the fibers.
One prior art solution to the problem involves the use of shims inserted into the slot to maintain a minimum slot size in the event the free end of the cantilevered lid member becomes deformed toward the body member. The use of such shims has been found to be unsatisfactory because no control is provided in cases where the deformation of the cantilevered lid member raises the free end away from the lid member. The shims have also been found to be unacceptable because of the maintenance burden and the difficulty of adjusting the slot size with the shims. There is a need for a blower having a slot adjustment mechanism which is readily adjustable and easily cleanable, and which can provide accurate control of the blower slot during operation in a high temperature environment. There is also a need for a blower having a positive slot adjustment, enabling precise and controlled movement in either the upward or downward directions.